In many applications of audio equipment, such as televisions, stereo amplifiers CD players and the like, music and other recorded (or live) material generally includes both loud passages and quiet passages. If the audio volume is high enough (such as in a noisy environment), both quiet and loud passages a sufficiently audible. However, if the volume is reduced, quiet passages may become inaudible and one's listening enjoyment is reduced.
A compressor may be inserted into the audio path. If the compressor has a fixed compression ratio, it may be turned on and off as desired by the listener. However, the fixed compression ratio may be adequate for only a limited number of listening situations. Moreover, turning the compressor on and off is an inconvenience to the listener. If the compressor has a variable ratio, not only may it be turned on and off as desired by the listener but the compression may be adjusted, as well. As is known, compression tends to reduce audio quality and should be used sparingly, if at all. Thus, an experienced listener should adjust the compression whenever the volume level is changed. And, an inexperienced listener (or one who doesn't like the inconvenience of dual adjustments) may simply leave the compressor off or leave it on with the compression set to some arbitrary ratio rarely, if ever, changing it.